#include <stdio.h>
//typedef int Int;
#define pi 4.0*atan(1.0)
int main(){
  double radius;
  double area;
  scanf("%lf", &radius);
  if (radius < 0)
    area =  - 1;
  else
    area = pi * radius * radius;
  if (area >= 0)
    printf("%.6f\n", area);
  else
    puts("Are you kidding?");
  return 0;
}
